Isn't the word "Unnie" quite unique???

"Unnie" is usually used mostly between women, right?
The original meaning of "Unnie" is a term used to
respectfully address someone older than oneself,
but in daily life, I see older women
calling younger female staff members
"Unnie" as well.
I've even seen older men go to a restaurant
and call a female server "Unnie-ya."
But on the contrary, men tend to never use the word
"Hyung" when addressing a stranger.
While "Unnie" is used quite extensively,
it seems like "Hyung" is a word used only among people who know each other.